/*
 * Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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/*
 * $Id: KeySelector.java,v 1.6 2005/05/10 15:47:42 mullan Exp $
 */
package javax.xml.crypto;

import java.security.Key;
import javax.xml.crypto.dsig.keyinfo.KeyInfo;
import javax.xml.crypto.dsig.keyinfo.RetrievalMethod;

/**
 * A selector that finds and returns a key using the data contained in a
 * {@link KeyInfo} object. An example of an implementation of
 * this class is one that searches a {@link java.security.KeyStore} for
 * trusted keys that match information contained in a <code>KeyInfo</code>.
 *
 * <p>Whether or not the returned key is trusted and the mechanisms
 * used to determine that is implementation-specific.
 *
 * @author Sean Mullan
 * @author JSR 105 Expert Group
 * @since 1.6
 */
public abstract class KeySelector {

  /**
   * The purpose of the key that is to be selected.
   */
  public static class Purpose {

    private final String name;

    private Purpose(String name) {
      this.name = name;
    }

    /**
     * Returns a string representation of this purpose ("sign",
     * "verify", "encrypt", or "decrypt").
     *
     * @return a string representation of this purpose
     */
    public String toString() {
      return name;
    }

    /**
     * A key for signing.
     */
    public static final Purpose SIGN = new Purpose("sign");
    /**
     * A key for verifying.
     */
    public static final Purpose VERIFY = new Purpose("verify");
    /**
     * A key for encrypting.
     */
    public static final Purpose ENCRYPT = new Purpose("encrypt");
    /**
     * A key for decrypting.
     */
    public static final Purpose DECRYPT = new Purpose("decrypt");
  }

  /**
   * Default no-args constructor; intended for invocation by subclasses only.
   */
  protected KeySelector() {
  }

  /**
   * Attempts to find a key that satisfies the specified constraints.
   *
   * @param keyInfo a <code>KeyInfo</code> (may be <code>null</code>)
   * @param purpose the key's purpose ({@link Purpose#SIGN}, {@link Purpose#VERIFY}, {@link
   * Purpose#ENCRYPT}, or {@link Purpose#DECRYPT})
   * @param method the algorithm method that this key is to be used for. Only keys that are
   * compatible with the algorithm and meet the constraints of the specified algorithm should be
   * returned.
   * @param context an <code>XMLCryptoContext</code> that may contain useful information for finding
   * an appropriate key. If this key selector supports resolving {@link RetrievalMethod} types, the
   * context's <code>baseURI</code> and <code>dereferencer</code> parameters (if specified) should
   * be used by the selector to resolve and dereference the URI.
   * @return the result of the key selector
   * @throws KeySelectorException if an exceptional condition occurs while attempting to find a key.
   * Note that an inability to find a key is not considered an exception (<code>null</code> should
   * be returned in that case). However, an error condition (ex: network communications failure)
   * that prevented the <code>KeySelector</code> from finding a potential key should be considered
   * an exception.
   * @throws ClassCastException if the data type of <code>method</code> is not supported by this key
   * selector
   */
  public abstract KeySelectorResult select(KeyInfo keyInfo, Purpose purpose,
      AlgorithmMethod method, XMLCryptoContext context)
      throws KeySelectorException;

  /**
   * Returns a <code>KeySelector</code> that always selects the specified
   * key, regardless of the <code>KeyInfo</code> passed to it.
   *
   * @param key the sole key to be stored in the key selector
   * @return a key selector that always selects the specified key
   * @throws NullPointerException if <code>key</code> is <code>null</code>
   */
  public static KeySelector singletonKeySelector(Key key) {
    return new SingletonKeySelector(key);
  }

  private static class SingletonKeySelector extends KeySelector {

    private final Key key;

    SingletonKeySelector(Key key) {
      if (key == null) {
        throw new NullPointerException();
      }
      this.key = key;
    }

    public KeySelectorResult select(KeyInfo keyInfo, Purpose purpose,
        AlgorithmMethod method, XMLCryptoContext context)
        throws KeySelectorException {

      return new KeySelectorResult() {
        public Key getKey() {
          return key;
        }
      };
    }
  }
}
